1. Field
Aspects of the present invention generally relate to a sheet feeding device and an image forming apparatus.
2. Description of the Related Art
Image forming apparatuses include sheet feeding devices that feed sheets. A known sheet feeding device includes a lifter mechanism that maintains the level of the upper surface of a stack of sheets on a stacking member to be at substantially constant, and a pickup roller that picks up one of the sheets that is at the substantially constant level.
Specifically, the sheet feeding device includes a sensor that detects whether or not the upper surface of the stack of sheets on the stacking member is at a feedable position (the substantially constant level). On the basis of a signal from the sensor, the stacking member is moved up and down. Thus, the level of the upper surface of the stack of sheets on the stacking member can be maintained to be substantially constant, and a stable sheet feeding operation can be performed.
However, if the stack of sheets is curled, the upper surface of the stack of sheets has level variations. In such a case, the sensor may incorrectly detect the level of the upper surface of the stack of sheets. Hence, a sheet feeding device is disclosed by Japanese Patent Laid-Open No. 2009-214966 in which, if it has been detected a plurality of times that the upper surface of the stack of sheets is not at the feedable position after the start of the sheet feeding operation, a control operation of lifting the stacking member is performed. Another sheet feeding device is disclosed by Japanese Patent Laid-Open No. 2009-215041 that includes a curl detecting mechanism and performs a control operation of moving the stacking member up and down in accordance with the size of the curl in the stack of sheets.
In yet another sheet feeding device, a feeding path extending from a manual feed tray (a second pickup member) and a feeding path extending from a cassette (a first pickup member) merge with each other at a position below a pickup roller that picks up one of the sheets in the cassette. In such a configuration, to feed a sheet from the manual feed tray (the second pickup member), the pickup roller that picks up one of the sheets in the cassette needs to be moved upward so that a conveyance path is provided.
The device disclosed by Japanese Patent Laid-Open No. 2009-214966 cannot be applied to the sheet feeding device in which the feeding path extending from the cassette (the first pickup member) and the feeding path extending from the manual feed tray (the second pickup member) merge with each other as described above.
This is because the device disclosed by Japanese Patent Laid-Open No. 2009-214966 is to detect the level of the upper surface of the stack of sheets in conjunction with the movement of the pickup roller, whereas the level of the upper surface of the stack of sheets cannot be detected in conjunction with the movement of the pickup roller in the sheet feeding device in which the two feeding paths merge with each other as described above.
In the device disclosed by Japanese Patent Laid-Open No. 2009-215041, a mechanism of lowering the stacking member at the detection of any curls is necessary, increasing the complexity and the cost of the device.